Precision electronic parts are being made smaller, and therefore have tighter tolerances. One area where this is particularly important is in the fabrication of flat tape heads.
Many tape heads have a top surface that is curved, defining the contact surface of the tape. One downside to this type of head is that each head must be fabricated individually. The tape bearing surface is rounded by moving the head back and forth in a pendulum-like motion in a viscous solution of diamond slurry. This is a very time consuming and expensive process.
Tape heads with a flat tape bearing surface, or flat heads, have recently emerged as an effective, yet less expensive alternative to rounded tape heads. FIG. 1 depicts one such tape head system 100. The head system includes of a pair of heads 102, each having a closure 104 that engages the tape 106 as it passes over the head. Each head is coupled to a block 108, which is in turn coupled to an actuator mechanism (not shown) of a tape drive system.
The pressure at which the tape engages the head affects the write/read performance and error rate. The wrap angle α, the angle that the tape is wrapped around the head, controls how the tape flies over the head, and thus, affects the pressure at which the tape engages the head. Slight variations from the design angle can result in significant degradations in performance. For example, if the specified wrap angle is less than one degree, a deviation of a few tenths or hundredths of a degree can have a large impact on write/read performance and error rate.
The flatness and relative angle of the top surface (tape bearing surface) 110 and bottom surface 112 of the head can affect the wrap angle of the tape over the head, and because the flat head works on the principle of wrapping the head at specific wrap angles, it is important to measure this parameter and disposition for it to within tenths, hundredths, or thousandths of a degree to verify that the head is within design tolerances.
Current measurement tools such as the Avant scope and optical technologies used in current manufacturing cannot achieve this accuracy. Nor are the results of these technologies repeatedly consistent. One reason that these technologies are inaccurate is because they do not take into account the way the bottom surface of the head actually sits on the actuator. Because the bottom surface of the head may be uneven, the head may sit at a slight angle when actually coupled to the actuator. This in turn will affect the wrap angle. Another reason that these technologies are inaccurate is because they do not take into account the reference surface that the part sits on during the measurement. Many technologies assume that the reference surface is perfectly flat. However, when trying to achieve accuracies of hundredths or thousandths of a degree, flatness is a relative term. A slight tilt or variation in the surface geometry of the reference surface can have significant effects on the angle that is measured.
What is therefore needed is a device and technique for measuring the flatness and relative angles of the top and bottom surfaces of the head reliably and accurately.